Nick Hull wrote:
In article , "Gimpy"
wrote:

Thanks HTH, but that article I believe was written for an engineer ? The
info I did get from it was stuff I already knew.. I am in a wheelchair & do
use an electric scooter outside the house & the scooter does like a
wheelchair use 2 U1 batteries in series for 24v. These things are pretty
expensive & last year I bought 2 new ones & they petered out in about 4
mo's. My son took them into the store where he bought them & they used some
type load tester to determine one OK & one dropped off after a min. or so.
Yr's warrt. so they gave me one new battery. What I was looking for was a
tester I could use here at the house as I now have a couple of spare
batteries & generally trade in 2 for 2 & just could be one of those I'm
trading in is still usable ?? This is why I was wondering about a
load/tester that would work & not damage anyrthing. Have been told car/truck
load testers are a no-no & could damage these batteries?? In anycase thanks
for your help. Gimpy

What you want is a meter to read the difference between the batteries
WHILE YOU ARE USING THEM. This is easily done with a small cheap
voltmeter (preferably center reading) and two equal resisters. Put the
resisters in series from +24v to (-) and connect the voltmeter from the
center of the pair of resisters to the center joining strap of the
batteries (+12 v nominal). The meter should read zero if the batteries
have the same voltage under load, and will deflect one way or the other
if one battery gets weaker than the other. You could use a cheap
digital and read + and - or a center zero analog of about +/- 4 volts or
so.

Or what I was thinking of was using two of those cheap meters. One
across each battery. Harbor Freight has some that would be good enough.
If during use one of the batteries drops more than the other some
corrective action might be needed such as a desulfation charge on that
battery.